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1 CHAPTER 2--ACIDS, BASES AND SALTS Acids: Substances which turn blue litmus solution red are called acids. Acids are sour in taste Bases: Substances which change red litmus solution blue are called bases. They are bitter in taste. Mineral Acids: Acids which are obtained from minerals like sulphates, nitrates, chlorides etc. are called mineral acids, e.g., H 2 SO 4 (Sulphuric acid), HNO 3 (Nitric acid) and HCl(Hydrochloric acid). Organic Acids: Acids which are obtained from plants and animals are called organic acids.e.g. citric acid, ascorbic acid, tartaric acid, lactic acid, acetic acid. Hydronium Ions: They are formed by reaction of H + (from acid) and H 2 O. It is because H + is unstable. Universal Indicator: A universal indicator is a mixture of indicators which shows a gradual but well-marked series of colour changes over a very wide range of change in concentration of H + ion. Strong Acids: Acids which dissociate into ions completely are called strong acids. Eg. H 2 SO 4, HCl Weak Acids: Acids which do not dissociate into ions completely are called weak acids Eg.. citric acid, acetic acid. 5

2 Chemical properties of acids (i) Acids react with active metals to give salt and hydrogen gas. (ii) Acids react with metal carbonate and metals hydrogen carbonate to give salt, water and carbon dioxide. (iii) Acids react with bases to give salt and water. This reaction is called neutralization reaction. (iv) Acids react with metals oxides to give salt and water. Chemical properties of Bases (i) Reaction with Metals Certain metals such as Zinc, Aluminiumand Tin react with alkali solutions on heating and hydrogen gas is evolved (ii) Reaction with acids Bases react with acids to form salt and water. Indicators - Indicators are substances which indicate the acidic or basic nature of the solution by their colour change. ph scale : A scale for measuring hydrogen ion concentration in a solution. The ph of a solution is defined as the negative logarithm of hydrogen ion concentration in moles per litre. ph =-log [H + ] ph =-log [H 3 O + ] where [H+] or [H 3 O + ] represents concentrations of hydrogen ions in solution. The ph of a neutral solution is 7 The ph of a acidic solution is < 7 The ph of a basic solution is > 7 Some Important Compounds and their uses Common Name Chemical name Chemical formula Uses Washing soda Sodium carbonate decahydrate Na 2 CO 3.10H 2 O Manufacture of borax, caustic soda, softening of hard water Baking soda Sodium hydrogen carbonate NaHCO 3 Used as antacid, ingredient of baking powder Bleaching powder Calcium oxychloride CaOCl 2 Bleaching clothes, used as oxidizing agent, disinfecting water, manufacture of chloroform Plaster of Paris Calcium sulphate hemihydrate CaSO 4. 1/2H 2 O Plastering fractured bones, making toys,decorative materials,statues EQUATIONS OF ACIDS,BASES AND SALTS Acid + Metal Salt + Hydrogen gas 6

3 H 2 SO 4 +Zn ZnSO 4 +H 2 Base+ Metal Salt + Hydrogen gas 2NaOH + Zn Na 2 ZnO 2 + H 2 (Sodium zincate) Base + Acid Salt + Water NaOH(aq) + HCl(aq) NaCl(aq) + H 2 O(l) Acids give hydronium ions in water HCl+H 2 O H 3 O + + Cl - Bases generate OH - ions in water NaOH(aq) + H 2 O Na + (aq)+oh - (aq) Reactions Of Important chemical compounds Preparation of Bleaching powder By the action of chlorine on dry slaked lime Ca(OH) 2+ Cl CaOCl 2 +H 2 O On heating, baking soda liberates CO 2 2NaHCO 3 Heat Na 2 CO 3 + H 2 O + CO 2 Washing soda(sodium carbonatedecahydrate) Na 2 CO H 2 O Na 2 CO 3.10H 2 O Plaster of Paris Preparation of plaster of Paris CaSO 4 2H 2 O 373K(Heat) CaSO 4.1/2 H 2 O +1.1/2H 2 O On mixing plaster of Paris with water,gypsum is obtained CaSO 4.1/2H 2 O +1 ½ H 2 O CaSO 4.2H 2 O 7

4 MIND MAP ACIDS BASE Acids,Bases and salts INDICATOR ph VALUE SALTS Washing soda Bleaching powder Baking soda 8

5 QUESTION BANK Very Short Answer Type Questions(1mark) 1. Write the name of the products formed by heating gypsum at 373K.Write one useof it. Plaster of Paris and water. It is used for plastering fractured bone. 2. Write the chemical name and formula of the compound which is used as an antacid. Sodium bicarbonate, NaHCO 3 Short Answer Type Questions(2mark) 1. Given below are the ph values of different liquids.7.0, 14.0, 4.0, and 2.0. Which of these could be that of a) lemon juice b) distilled water c) sodium hydroxide solution d) tomato juice. 2. What is baking powder? How does it make the cake soft and spongy? Baking powder is a mixture of sodium hydrogen carbonate and tartaric acid. On heating it liberatesco 2 which makes the cake soft and spongy Short Answer Type Questions(3mark) 1. Write the chemical name of Plaster of Paris. Write a chemical equation to show the reaction between Plaster of Paris andwater. Name the compound produced in this reaction. Calcium Sulphate hemihydrate. CaSO 4. 1 / 2 H 2 O +1 1 / 2 H 2 O CaSO 4.2H 2 O The compound produced is Gypsum. 2. A gas X reacts with lime water and forms a compound Y which is used as bleaching agent in the chemical industry. Identify X and Y.Give the chemical equation of the reaction involved. X is chlorine Y is CaOCl 2 (calcium oxy chloride) used as bleaching agent. Ca(OH) 2 + Cl CaOCl 2 +H 2 O Long answer type questions (5 mark) 1. a) A milk man adds a very small amount of baking soda to fresh milk.why does he shift the ph of the fresh milk from 6 to slightly alkaline? b)mention ph range within which our bodyworks? c) Explain how antacids give relief from acidity. d) Mention the nature of tooth pastes.how do they prevent tooth decay? a) It is done to prevent the formation of lactic acid which spoils the milk b)ph range c)antacids neutralizes excess of acid in our body and gives relief. d) Basic. Neutralize the acid formed in the mouth 2. a) Crystals of a substance changed their color on heating in a closed test tube but regained it after some time when they were allowed to cool down. Name the substance and write its formula.explain the phenomenon. b) How is sodium carbonate prepared? Give two uses of the compound a ) Copper sulphate,cuso 4.5H 2 O. It is blue. It becomes white on heating due to loss of water molecule. CuSO 4.5H 2 O Heat CuSO 4 +5 H 2 O It regains its colour by absorbing water from atmosphere CuSO H 2 O Heat CuSO 4.5H 2 O b) Prepared by passing CO 2 through ammoniacal brine Used for production of washing powder& manufacture of glass 9